Description of the Prior Art
In methods which depend on the biospecific effect between proteins and their corresponding substrates, it is advantageous to use the proteins in the form of a solid carrier-bound or immobilized form. The proteins can thus be separated from the substrate solution quite easily by filtration. Carrier-bound proteins have importance in affinity chromatography and especially in the carrying out of enzymatic processes, wherein the carrier-bound protein is an enzyme.
Carrier-bound proteins are generally characterized by higher stability against inactivation due to shifts in pH values, higher temperatures and higher stability against autooxidation as compared with free proteins in aqueous solution. Nevertheless, a decrease in the biospecific activity--such as in the case of enzymes the enzymatic activity--is observed after multiple uses of the carrier-bound proteins.
It is known that one can stop, or even decrease, the activity loss of proteins by treatment with various mercaptans (see for example Dissertation of Jan Carlsson, Uppsala, 1974, page 8, Abstract). The effectiveness of the mercaptans is presumed to be a result of their ability to split disulfide bridges which resulted by autooxidation of thiol groups. Autooxidation is thus generally seen as the cause of the reversible loss in activity.
In most cases, however, it is not desirable to add a mercaptan to a substrate solution to maintain the activity of bound proteins, since to do so would adversely affect the purity of the substrate solution, and would require a purification step. Separate reactivation of carrier-bound proteins between successive runs is generally not satisfactory since it encompases additional expense and most mercaptans are toxic and foul-smelling.